Isotopic fingerprints of the Lake Żabińskie (NE Poland) hydrological system on contemporary carbonates precipitated in the lake.

An isotopic monitoring was undertaken in 2012-2014 at Lake Żabińskie (Mazurian Lakeland, NE Poland). The aim was to identify the factors and processes controlling an isotopic composition of the lake water and to explore the mechanism responsible for recording the climatic signal in stable isotope composition of deposited carbonates. δ18 O and δ2 H in the precipitation, lake water column, inflows and outflow, δ18 O and δ13 C in the carbonate fraction of sediments trapped in the water column were recorded with monthly resolution. A relationship between δ18 O and δ2 H in local precipitation was used to estimate the local meteoric water line. The dataset obtained for the water enabled to identify the modification of the water's isotopic composition due to evaporation, connected with seasonal lake water stratification and mixing patterns. Statistically significant correlation coefficients suggest that the δ18 O of the carbonate fraction in the sediment traps depends on the δ18 O of rainfall water and on air temperature. The fractionation coefficient α shows that in summer months the carbonate precipitation process is closest to equilibrium. As expected for an exorheic lake, no significant correlation was observed between δ18 O and δ13 C in precipitated carbonate.